How do I know if my disc rotors are worn?

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  • How do I know if my disc rotors are worn?
  • I_Ache

    Sounds like a stupid question I know but I have never replaced worn rotors.
    I have some SH (from here) old style Hope Mono Minis the black and gold ones. After swapping the wheels today I noticed that there is a groove running all the way round both discs. Its had to explain where the groove is, its on the arms that connect the centre of the rotor (where the bolts are) to the outer braking surface. It looks like the pads have been using these arms for braking and not just the outer circular bit is this normal?

    I think his may be causing my front brake to have excessive leaver travel. I dont have any other discs this size or know anybody who has and dont want to just go and buy new rotors to try it out. Does anybody have any experience with this.

    BTW I am not complaining about the sale or the condition the brakes were in when I got them just trying to diagnose the problem.

    Thanks all.

    There will be a minimum thickness advertised for the rotors. If you can feel a ridge where you do then they are worn but worn out? Hard to tell without measuring to spec. It will not cause excessive lever travel as the calipers should self adjust. Likely to be a sticky piston

    when the braking surface wears through. but that depends on whether your prepared to crash when they do evenryaly give up.

    I’ve got some very thin hayes rotors that are still going fine.


    I have got that ridge on my old Julie disc rotors – it’s on the arms that join the actual rotor to the 6-bolt part of the disc, just inside the rotor itself.
    It was caused on mine by a dimple on the ear of the Julie pads. It seems to be some kind of wear indicator, as when the pads get down to this level, the dimple starts pinging on the arms of the rotor. As the pad backing metal is so soft though, it is more cosmetic damage than a serious amount of wear.


    This is on both discs. Both pistons on the front brake seem to be moving freely but I will have a closer look. At first I thought there may not be enough fluid in the system but now I’m not sure.

    Premier Icon steveh

    NOt enitrely helpful but if you do want some new ones they can be pretty cheap from these guys, good service too.

    How worn are the pads? If the pads are decent then the relatively small amount of missing rotor shouldn’t be an issue. If the pads are knackered as well it can make a minor problem worse.


    The pads have a good 3mm left on them but there is a bit of rust on the one side of the rotor that I just noticed. Could this be a sign of a sticky piston?


    You know your discs are worn when they rip off the spider and crumple up like a piece of tin foil. Until then I wouldn’t worry.


    Scoring or blue tint of over heated braking?

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